It is known that the skin is permeable to certain compounds, such as nitroglycerine and scopolamine; or the skin could be made more permeable by other means, such as by the use of solvents, or other types of enhancers, such as physical means or chemical enhancers. Thus, presently the rate of drug delivery is controlled by a semi-permeable membrane, for example, in an osmotic profusion type drug applicator. Such drug applicators are currently marketed and in use for the transdermal delivery of nitroglycerine and scopolamine. These systems, however, are limited just to drugs which are soluble in both water and oil, are of low molecular weight, and are potent in small concentrations. Consequently, there are very few drugs which can be utilized with this modality of delivery. In addition, it is very difficult to consistently produce a membrane or a matrix which ensures a predictable rate of drug delivery.
The delivery of a drug from a drug reservoir can be accomplished by electrokinetic effect, that is, either by iontophoresis, electrophoresis or by electro-osmosis. Further, the rate of delivery is affected by the amount of electric current applied between the skin and the drug reservoir. Further, the electric current affects both the skin of the patient and the drug reservoir independently so as to create conditions that increase or decrease the rate of delivery of the drug through the skin of the patient. For example, current will affect the pH of the skin at the interface between the membrane of the reservoir, or patch area. Also, a polarization of the skin will change skin permeability. The charge of the drug particles, or ionic charge, will cause repulsed direction of the ionized drug through the skin. Also, an electro-osmotic effect is created at the skin surface or mucous membrane by electric current. As for the drug reservoir of the patch, electrical current passed through the drug, which is contained in the drug reservoir, can control or improve mobility of the drug thus allowing less current to be needed for drug movement into the skin or mucous membrane. Also, the natural diffusion of the drug compound acts within the patch and is controlled in either additive or subtractive fashion by sending an electric current through the drug independently of the current through the skin; the rate of delivery and the degree of concentration of the drug at the skin can be affected and independently controlled. Also, the pH of the drug within the patch near the skin can thus be changed by electric current. Also, electric current in the patch can cause electrolysis, thus activating in sequence pre-existing buffering agents in the drug reservoir. In summary, control of the rate of delivery of a drug from a drug reservoir through the skin can be controlled by independent but simultaneous currents through the patch and through the skin. It is hereby noted that descriptions relating to mass transfer activity by application of electric current is contained in the applicant's earlier filed U.S. patent applications, Ser. Nos. 524,252, 660,192, PCT/US/85/00080, 702,486, and my application Ser. No. 000,555, filed Jan. 5, 1987, entitled "Programmable Control and Mounting System for Transdermal Drug Applicator", filed concurrently herewith as co-inventor. All of the disclosures contained in these earlier filed U.S. patent applications are hereby expressly incorporated herein by reference.
It is therefore an object of the present invention to control the rate of delivery of a drug from a drug reservoir by placing a plurality of electrodes within the reservoir in electrical circuit means with first and second power sources and with the skin or mucous membrane, the patch of the first power source being optionally directed to one of the two electrodes so as to cause the second power source to be added or subtracted from the first power source for current directed through the skin.